Amplifier



Sept. 4, 1928. 1,683,134

A. W. HULL AMPLIFIER Filed Dec 28. 1921 Albert VV. Hull, MQW' b5 His Attorneg.

Patented Sept. 4, 1928.

UNITED STATES PATENT OFFICE.

ALBERT W. HULL, OF SCHIENEC'LADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A` CORPORATION F NEW YORK.

AMPLIFIER.

Application nied December 28, 1921. Serial No. 525,366.

My present invention relates to amplifiers, and more particularly to amplifiers ofthe four-electrode, electron discharge type.

The object of my invention is to provide an improved apparatus and circuit connec' tion whereby a high degree of amplification can be secured with a device of the type referred to. A further object of my invention is to provide a system adapted to amplify currents of very high frequency with the same efficiency as currents of lower radio frequency.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended'claims. My invention itself, however, both as to its organization and method of operation, will best be understood by reference to the following description taken in connection with the accompanying drawing in which Figs. 1 and 2 show diagrammatically two diiferent circuit organizations whereby my invention may be carriedinto effect; Figs. 3 and 4 are cross sectional views of different modifications of four-electrode devices which may be employed in carrying out my invention; Fig. shows characteristic curves illustrating the operation of my invention, and Fig. 6 shows a circuit organization in-which certain features of the arrangements of Figs. 1 and 2 are combined.

In the arrangement shown in Fig. 1 I have indicated an electron discharge device comprising an electron emitting cathode Lacontrol electrode 2 surrounding the cathode, and electrode 3 surrounding the cathode and control electrode, and an electrode 4 surrounding the other electrodes, all of these electrodes being enclosed in anevacuated receptacle 5. This device is preferably constructed, as described and claimed in my copending application Serial No. 472,139, iiled May 24, 1921. The electrode 3 is made up of a plurality of flat strips or slats 6 either spaced in radial planes about the cathode, as shown in Fig. 3, or extending at an angle to the radial planes, as shown in Fig. 4. Circuit connections are provided between the cathode and each of the other electrodes, the connection between the cathode and control electrode including the secondary 7 of a.

transformer in the primary 8 of which the currents to-be amplied'are cause to flowv The battery 9 is included in the circuit connection between the cathode and anode 4 and furnishes the necessary potential for the operatlon of this circuit.- A portion of the battery 9 which may be varied by means of the adjustable connection 10 is included in the circuit between cathode and slat electrode 3. The circuit between cathode and anode also includes a telephone receiver 11 or other suitable indicating device for producing an indication of amplified currents flowing in that circuit. f

When the electron discharge device is 'pass the control electrode 2 will be deiected to such an extent that they will strike the slats 6, their paths being indicated by the dotted lines e in Fig. 3. If the potentials applied to electrodes 3 and 4 are properly chosen each primary electron which strikes the slats will by its impact liberate secondary or impact electrons which' escape and iiow to the more positive electrode 4. By proper design of the apparatus and proper proportion of the potentials each primary electron striking the slats will be able to liberate several impact electrons so that the total number of electrons reaching the anode 4 and hence the currentiiowing in the circuit connection to anode 4 will be much greater than the current emanating fromcathode 1. In order to produce the magnetic field necessary for this operation a separate source of current may be connected to a coil surrounding the tube 5, or a coil 12 may be included in the circuit between the cathode and anode 4, this coil being wound around the recep-v tacle 5, as indicated in Fig. 3. A. substantially constant current will be caused to flow through the coil 12 and the variable component of the current in the circuit between cathode and anode may be bypassed around this coil 12 by means of a shunting condenser 13. In case the slats are arranged as shown in Fig. 4, and extend at such an angle as to be interposed in the direct paths of all of the electrons flowing from the cathode to the` anode the electrons flowing from the cathode 1 toward the anode il will practically all strike the slats 6 and hence the magnetic field may with this construction be dispensed with.

By the arrangements which I have described it is possible to secure a much higher degree of amplification than with the usual three-electrode device. The current' between the cathode 1 and the slat electrode 3 will be controlled by the control electrode 2 in the same manner as intheordinary three-electrode device and the current variations set up inthe secondary 7 will be amplified. The amplified variations inthe current to the slat electrode 3 will be further amplified in the circuit of the anode 4 by a factor equal to the average number of secondary electrons produced by one primary electron striking .the slots 6. i

' In the arrangement thus far described, no advantage is taken of the negative resistance characteristic produced in the circuit of slat electrode 3 by reason of the fact that .more

impact electrons are emitted therefrom than the primary electrons received. In the arrangement shown in Fig. 2 I have indicated a positive resistance 14, in the circuit of the slat electrode 3 for balancing the negative resistance of the circuit. The use of positive resistance in s'teries with negative resistance in this manner. is well known, being fully describedin my prior U. S. Patents, 1,385,- 873, July '26, 1921, an d`1,387,984, August 16, 1921. i

A device constructed inthe manner I have indicated, however, is especially adapted for use in this manner as I have found that the negative resistance portion of the characteristie current curve to the electrode 3 is practically straight over a wide range which makes it comparatively easy to balance negative resistance ver closely with positive resistance, andthereli give a high degree of amplification over a wide operating range.

In Fig. 5 I have indicated two typical l curves showing the relation between the current to the slat electrode and the potential thereof. The curves A and B represent this relation for two different values of potential of the control electrode 2. Dotted line C represents the variation of current in the positive resistance with variations in potential of the slat electrode, and this resistance may be so chosen that curve C will have '.'ery nearly the same slope as the curves Al and B over a wide operating range, this being the condition necessary to secure a high I degree of amplification.

Diiiiculty has been experienced in amplifying very high frequency currents by means of the usual three-electrode amplifierbecause ofthe capacity existing between the anode and the control electrode. In these threeelectrode devices an increase in grid voltage causes a decrease in plate or anode voltage and because of the capacity between grid and plate this decrease in the plate voltage opposes an` further increase in the grid voltage. In tje device which is operated as I have described, however, an increase in the grid voltage produces an increase 1n the voltage of the electrode 3 and this in turn by reason of the capacity between the electrodes tends to cause a further increase in the grid voltage and thus increase the amount of aniplification secured instead of decreasing it as in the three-electrode device. It will of course be understood that positive resistance 14, if desired, may be employed in the circuit arrangement shown in Fig. 1, and also that in case a device like that shown in Fig. is employed in the circuit arrangement shown in Fig. 2, the magnetic field may be produced in the manner illustrated in Fig. 1 for causing the electrons to strike the slats. VThe manner in which these diiferent features may be combined is shown diagrammatically in Fig. 6.

lV hat Iclaim as new and desire to secure by Letters Patent of the United States is 1. Means for amplifying electric currents comprising an electron discharge device having an electron emittin cathode, a control electrode, an anode an an electrode made up of conducting slats between said cathode and anode, circuit connections between said cathode and each of the other electrodes, means for causing the greater part of the i primary electrons emitted from said cathode to strike the slat electrode and produce an emission of impact electrons greater than the primary emission, means for impressing the currents to be amplified upon the circuit between cathode and control electrode, and means for producing an indication of the amplified currents flowing in the circuit connection to the anode.

2. Means for amplifying electric currents comprising an electron discharge device having an electron emittin cathode, a control electrode, an anode an an electrode made up of conducting slats between said cathode and anode,circuit connections between said cathode and each of the other electrodes, means for producing a magnetic field in the space between the cathode and anode to cause the greater part of the primary electrons emitted from said cathode to be delected so as to strike the slat electrode and produce an emission of impact electrons reater than the primary emission, means o r impressing the currents to be amplified upon the circuit between cathode and control electrode, and means for producing an indication of the amplified currents flowing inthe circuit connection to the anode. y

3. Means for amplifying electric currents comprising an electron discharge device havand anode, circuit connections between said' cathode and each of the other electrodes, means for producing by current flowin in the circuit between cathode and ano e a magnetic field in the space between the cathode and anode to cause the greater part of the primary electrons emitted from said cathode to be deflected so as to strike the slat electrode and produce an emission of impact electrons greater than the primary emission, means for impressing the currents to be amplified upon the circuit between cathode and control electrode, and means for producing an indication of the amplified currents flowing in the circuit connection to the anode.

4. Means for amplifying electric currents comprising an electron discharge device having an electron emitting cathode, 'a control electrode, an anode and an electrode made up of conducting slats between said cathode and anode, circuit connections between said cathode and each of the other electrodes, means for causing the greater part of the primary electrons emitted from said cathode to strike the Slat electrode and produce an cathode, a control emission of impact electrons greater than the primary emission thereby producing a negative resistance in the circuit between cathode and Slat electrode, a positive resistance in that circuit of substantially the same value as the negative resistance, means for impressing the currents to be amplified upon the circuit between cathode and control electrode, and means for producing an indication of the amplified currents flowing in the circuit connection to the anode.

5. The combination in an apparatus of the class described of an evacuated receptacle containing an electron emitting cathode, a control electrode adjacent said cathode, an electrode surrounding said cathode and control electrode made up of conducting slats and an anode surrounding said slat electrode, means :for producing an emission of impact electrons from said slat electrode which is greater than the primary emission from the cathode, and means for impressing a variable potential upon the control electrode to vary the emission from the slat electrode.

In witness whereof, I have hereunto set 5 

